Molybdenum disulfide has long been known as a desirable additive for use in lubricating oil compositions. However, one of its major detriments is its lack of oil solubility. Molybdenum disulfide is ordinarily finely ground and then dispersed in the lubricating oil composition to impart friction modifying and antiwear properties. Finely ground molybdenum disulfide is not an effective oxidation inhibitor in lubricating oils.
As an alternative to finely grinding the molybdenum disulfide, a number of different approaches involving preparing salts of molybdenum compounds have been tried. One type of compound which has been prepared is molybdenum dithiocarbamates. Representative compositions are described in U.S. Pat. No. 3,419,589, which teaches molybdenum (VI) dioxide dialkyldithiocarbamates; 3,509,051, which teaches sulfurized oxymolybdenum dithiocarbamates; and 4,098,705, which teaches sulfur containing molybdenum dihydrocarbyl dithiocarbamate compositions.
An alternative approach is to form dithiophosphates instead of dithiocarbamates. Represenatative of this type of molybdenum compound are the compositions described in U.S. Pat. No. 3,494,866, such as oxymolybdenum diisopropylphosphorodithioate.
U.S. Pat. No. 3,184,410 describes certain dithiomolybdenyl acetylacetonates for use in lubricating oils.
Braithwaite and Greene in Wear, 46 (1978) 405-432 describe various molybdenum-containing compositions for use in motor oils.
U.S. Pat. No. 3,349,108 teaches a molybdenum trioxide complex with diethylenetriamine for use as an additive for molten steel.
Russian Pat. No. 533,625 teaches lube oil additives prepared from ammonium molybdate and alkenylated polyamines.
Another way to incorporate molybdenum compounds in oil is to prepare a colloidal complex of molybdenum disulfide or oxysulfides dispersed using known dispersants. U.S. Pat. No. 3,223,625 described a procedure in which an acidic aqueous solution of certain molybdenum compounds is prepared and then extracted with a hydrocarbon ether dispersed with an oil soluble dispersant and then freed of the ether. U.S. Pat. No. 3,281,355 teaches the preparation of a dispersion of molybdenum disulfide by preparing a mixture of lubricating oil, dispersant, and a molybdenum compound in water or C.sub.1-4 aliphatic alcohol, contacting this with a sulfide ion generator and then removing the solvent. Dispersants said to be effective in this procedure are petroleum sulfonates, phenates, alkylphenate sulfides, phosphosulfurized olefins and combinations thereof.